Cutting devices have been known for a long time. They are used primarily for cutting printed paper webs, such as are required by large companies in the service field, such as in the finance or insurance sector and administrative companies. These are high-performance paper processing devices which encompass inter alia performance cutting devices and which are designed for operation with the greatest possible level of automation.
To ensure reliable operation at such high throughputs and speeds, it is necessary to take various precautions. For example, smooth and reliable guidance of the paper web is of primary significance. Another problem lies in the supply of paper to the cutting device: to be able to carry out reliable transverse paper severing with a quality adequate for all purposes, and in particular without tear traces, the paper web must be stopped for a brief moment before and during the transverse severing. As a result, the paper web must be moved at different speeds, or passes through different phases of movement, at the location of the transverse severing device. Aside from a phase of constant speed, which in practical operation may be arbitrarily short or negligible, phases of acceleration and a phase of braking to a standstill are also required. This results in an average speed which corresponds to the speed of the paper supply and which constitutes the operational speed of the continuously operating device.
Because said high-performance cutter should operate as continuously as possible and with the least possible interruption, measures must be taken to ensure that the paper web accumulates (braking or holding phase) in a certain region of the processing train or of the cutting device, before the accumulated material is depleted and normal movement (constant speed) is resumed after transverse severing has taken place. Here, it must be ensured that in particular the manner of acceleration does not lead to tearing of the paper web.
DE 100 11 006 discloses a device for cutting paper webs, having a paper deceleration device which is operated by a blower and in which the paper web is guided by means of an air flow, which acts from an underside of the web, through an upwardly directed loop.
The web deceleration, in a device for cutting paper webs, described in EP 1 268 329 or WO 01/66448 is based on precisely this described principle.
Furthermore, EP 1 741 653 describes that, firstly, the paper web is cut longitudinally and, subsequently, the two separate webs are supplied to the transverse severing device via a large, loosely hanging loop. In this device, owing to the relatively large loop, there is the risk of uncontrolled paper supply, and therefore jamming and crumpling.
It is likewise important in this context that, in the following transverse cutting device, the paper webs are stopped only for a very short time for the cutting process, that is to say the transverse severing process must take place as rapidly as possible such that no unnecessary and excessive paper build-up occurs in the supply.
It is therefore a first object of the invention to provide a device in which the coupling of the at least approximately continuous operation at the paper infeed point to the discontinuous operation at the transverse severing device is realized in such a way that no slipping, crumpling or even tearing of the paper web occurs. It is also important that, as a result of the longitudinal severing of the paper web and therefore the merging of the two web parts, the resulting different advancement of the web parts is compensated.
It is a further object of the present invention to keep the interruptions in the discontinuous part, that is to say during the transverse severing, as short as possible and thereby accelerate the take-off off the cut paper.
According to the present invention, there is correspondingly proposed a device for cutting paper webs, having a substantially continuously operated region of the paper supply, a discontinuous region of transverse severing of the paper web, and a buffer region for coupling the regions.
It is proposed that the buffer region which is possibly provided downstream of the longitudinal cutting point between the continuous and discontinuous regions and which serves for coupling the continuous and discontinuous regions has at least one upwardly open, box-like receptacle into which the paper web or paper webs is or are guided in a hanging, looped manner.
A negative pressure can be generated in the receptacle such that the paper web is driven or pulled into the receptacle and if appropriate against the side walls.
It is however also possible for a blower to be provided in the region of the orifice in order to drive the paper web into the receptacle.
In one design variant, the buffer region is arranged downstream of a longitudinal cutting device at which at least two longitudinal webs are produced, whereby at least two separate webs running adjacent to one another are guided in the receptacle, or the two webs are guided in two receptacles arranged adjacent to one another. The arrangement of the buffer region downstream of a longitudinal severing device makes allowance for the problem of two web parts being guided with possibly different advancement to the transverse severing device. Improved buffering between the continuous and discontinuous operation even of the separately moved paper webs is thus ensured.
It is in turn proposed, in a further design variant, that a dividing device such as a dividing screen is provided centrally between the loops of the paper webs in order to prevent adhesion of the loops in the center.
If the one or more receptacles have a U-shaped cross section, it is for example possible for suction orifices and/or a suction fan in the base of the receptacle for the purpose of generating a negative pressure in order to pull the paper webs downward. It is however also possible for suction elements to furthermore be provided in the side walls of the receptacle in order to pull the paper webs against the side walls.
If for example three or more longitudinal webs are produced, it is correspondingly possible for the paper webs thus produced to be looped and pulled into one receptacle, or else three or more receptacles may correspondingly be arranged adjacent to one another or offset with respect to one another in order to pull the respective paper webs into the receptacle for compensation.
In a further design variant of the present invention, it is proposed that, following the buffer zone or the abovementioned receptacles, a so-called braking zone is provided by virtue of a negative pressure being generated along, for example below, the paper webs emerging from the receptacle or receptacles, so as to thus prevent an uncontrolled paper movement. Since the paper webs exiting the buffer zone are briefly stopped and accelerated again in the region of the transverse cutting point, there is the risk of so-called overshooting as the paper webs emerge from the above-described vacuum box, which may lead to bulging or tearing of the paper webs. For this reason, it is proposed according to the invention that for example suction holes are provided, in each case following the so-called vacuum box, in the surface over which the paper webs pass, by means of which suction holes a negative pressure can be generated below the paper web. The negative pressure generated is coupled in terms of control to the transverse cutting process or the transport rollers positioned upstream of the transverse cutting process, such that upon the stopping of the transport or during the paper deceleration, a braking action is generated by means of the negative pressure. During the acceleration of the paper, the negative pressure is eliminated such that the braking action is eliminated, and acceleration can be effected with little force and low web loading.
A further measure according to the invention is proposed in the region of the transverse severing device, for the purpose firstly of guiding one or other or both paper webs optimally into the region of the transverse severing point, of increasing the cutting accuracy, and of removing the cut papers from the cutting region as rapidly as possible and without traces of abrasion. It is proposed here that a transport device positioned downstream of the transverse severing device can be controlled such that it can be at least temporarily deactivated during the feed movement of the paper web imparted by a transport device positioned upstream of the transverse severing device, in such a way that the paper web can be introduced into the region of the transverse severing point without resistance. During or shortly after or shortly before the transverse severing process, said downstream transport device is activated in order to transport the cut paper away. Said transport device may be composed for example of two rollers or drums which engage with one another in order to impart a transporting movement, wherein one drum or roller can be moved away from the other during the introduction of the paper web and is driven against the other roller or drum during transverse severing or shortly after transverse severing has taken place or shortly before transverse severing takes place.
The transverse severing preferably takes place by means of a cutting element which has at least two cutting edges, in such a way that transverse severing of the paper web can be effected during every movement of the cutting element, that is to say upward or downward. Reference is made to WO 2004/018167 which describes a transverse severing device of said type which, in combination with the measures proposed according to the invention, is likewise a constituent part of the present invention.
It is finally proposed that a combining device be provided in the region between the buffer region and transverse severing point, said combining device having oblique sliding tubes and serving to arrange the at least two parallel-running, previously longitudinally severed paper webs so as to run one on top of the other. The sliding tubes are preferably provided with blow air means for preventing smearing or adhesion of the paper webs. Further preferred design variants of the device according to the invention are disclosed hereinafter.
Also proposed is a method for cutting paper webs as described further below. Further design variants of the method according to the invention are also disclosed as set forth in the following Detailed Description.